1. Field of the Invention
The present invention relates to a liquid jet recording head that ejects liquid such as ink onto a recording material such as recording paper and thereby performs a recording operation.
2. Description of the Related Art
As a typical liquid ejecting technology in use in liquid jet recording heads, there is known a technology in which ink is heated by an electro-thermal conversion element having a heating resistor, and ink is ejected by the action of film boiling. In a liquid jet recording head using electro-thermal conversion elements, the electro-thermal conversion elements are provided in liquid chambers filled with ink. By supplying the electro-thermal conversion elements with an electric pulse serving as a recording signal, and making the electro-thermal conversion elements generate heat, ink is provided with thermal energy. A change of phase of ink causes bubbling (boiling) of ink. Using the bubble pressure, ink is ejected through ink ejection ports, and recording is thereby performed on a recording material. An ink jet recording apparatus having such a bubble jet recording head that causes film boiling in ink and ejects ink using expansion and contraction of a bubble, can output high-quality characters and/or images at low cost.
Such a liquid jet recording head is configured by joining an orifice plate having a plurality of ink ejection ports, to a substrate. In the middle of the substrate is formed an ink supply port for supplying ink to the orifice plate. On the surface of the substrate to which the orifice plate is joined, are provided a plurality of electro-thermal conversion elements corresponding to the ink ejection ports. The ink supply port is connected with the ink ejection ports above the electro-thermal conversion elements by ink flow passages. Ink is supplied from the ink supply port to the ink flow passages, and is ejected through the ink ejection ports by the pressure of bubbles generated by the action of the electro-thermal conversion elements.
Such a method for making a liquid jet recording head is disclosed in Japanese Patent Laid-Open Nos. 10-157150 and 11-138817. Specifically, first, a soluble resin layer is formed on a substrate on which electro-thermal conversion elements are formed. Next, on this resin layer, a covering resin layer constituting an orifice plate is formed, for example, by spin coating. Next, ink ejection ports are formed in the covering resin layer. Finally, an ink supply port is formed in the substrate, and the soluble resin layer is dissolved. The dissolved parts serve as ink flow passages that connect the ink supply port with the ink ejection ports above the electro-thermal conversion elements.
In a liquid jet recording head made as above, the orifice plate is significantly stressed, for example, by contraction of the covering resin layer due to thermal hardening, and the orifice plate is prone to peel from the substrate. Such peeling becomes significant with increasing length of the liquid jet recording head or increasing thickness of the orifice plate.
A measure against such peeling of the orifice plate from the substrate is disclosed in Japanese Patent Laid-Open No. 2003-80717. Specifically, a groove is provided in the orifice plate to reduce the volume of the orifice plate, to reduce the stress on the orifice plate, and to make peeling unlikely. Making the shape of the groove saw-toothed is also effective in making peeling unlikely.
As described above, reducing the absolute volume of the orifice plate by providing a groove in the orifice plate is effective against peeling of the orifice plate from the substrate. However, when a groove is provided in the orifice plate, each end of the groove is significantly stressed. In some cases, slight peeling can occur at each end of the groove. Similarly, the edge of the orifice plate is also significantly stressed. In some cases, slight peeling can occur. If a peeling at one end of the groove and a peeling at the edge of the orifice plate join, this can develop into a larger peeling.
That is, when providing a groove in the orifice plate, attention needs to be paid to the position of each end of the groove. In particular, when at the edge of the substrate is provided a test terminal for measuring the characteristics of a circuit for driving the electro-thermal conversion elements, peeling of the orifice plate from the substrate near the test terminal is undesirable. Basically, the test terminal is covered by the orifice plate so as not to be exposed to ink and/or moisture.
When an electrode for supplying electric power to electric wiring is located near the test terminal, the area is sealed with a sealing material that consists primarily of epoxy resin. As a result, the edge of the orifice plate is often covered with the sealing material. However, when the edge of the orifice plate peels from the substrate, and when the peeling edge of the orifice plate is not sufficiently covered with the sealing material, there is a possibility that the test terminal can be exposed to ink and/or moisture. The test terminal often has a large potential difference relative to GND (ground), and contact with ink and/or humidity can lead to corrosion. However, corrosion does not instantaneously affect the performance of the liquid jet recording head.